Rather than laboriously trying to get the colour you want from the colours.xml file by modding and modding over hours and hours on end, I have come up with an idea I pictured in my own mind. The user clicks on the Colour Themes (found in Settings), and there are sliders that you can drag that change the colour of the interface, showing a preview, and each is labeled R (Red), G (Green), B (Blue), and when you are happy with your custom colour theme, you can save it in the game, in which it appears in your colour theme selection. There is a colour theme that has a button on it saying "Custom" with a darkened background around the button meaning that you can create a custom colour theme. You can colour almost everything in the game, down to the piano keyboard. This would be a rocking addition to the game! Plus, you will avoid errors, as you aren't messing with the xml files either, and can be used on mobiles.

With a variable color theme like that, the relative brightness/darkness of elements would have to stay relatively similar. So we could get away with just a simple hue slider (or at worst, hue + saturation).